Put a piece of tape on the solenoids that are stuck on. Then unplug the Pianocorder, wait 60 seconds, and disconnect the leads for those two solenoids from the driver board. (Leave them disconnected until the board has been repaired so that these solenoids don't overheat.)

The bass driver board has 32 solenoids connected to it. Tell us the plug position numbers of the two notes that are stuck on (counting from left to right) and we can pinpoint the parts that need to be replaced. (The lowest four notes of a piano are not played by the Pianocorder, so if you say notes #18 and #19 are stuck on, I assume this means positions 14 and 15 on the driver board are the ones that are bad. Right?)